RrLBD40 Enhances Salt Tolerance in Rosa rugosa via Promoting Root Development

LATERAL ORGAN BOUNDARIES DOMAIN (LBD) genes encode plant specific transcription factors that regulate various developmental processes and abiotic stresses. In this study, we characterized RrLBD40 from Rosa rugosa as a nucleus-localized transcription factor harboring a conserved LOB domain. We generated RrLBD40-overexpressing Rosa rugosa plants and compared them with control plants in terms of physiological indices, root architecture, and Na+ homeostasis. The results showed that RrLBD40 overexpression significantly increased peroxidase activity and reduced malondialdehyde content in the roots, indicating enhanced antioxidant capacity under salt stress. Furthermore, RrLBD40 overexpression markedly promoted root growth and development, a similar phenotype consistently observed in RrLBD40 transgenic Arabidopsis plants. Propidium iodide staining and analysis of the Na+ flux rates of root tips revealed that the barrier function of the Casparian strip was compromised in both the RrLBD40-overexpression and control plants under salt stress. This disruption of endodermal selectivity permitted Na+ influx into the vascular cylinder. Furthermore, neither plants exhibited significant Na+ efflux capacity. Taken together, these findings demonstrate that RrLBD40 enhances salt tolerance in Rosa rugosa by primarily promoting root growth and development, rather than modulating Na+ homeostasis.